DESCRIPTION (Investigator's Abstract): This proposal outlines a research program whose goal is to determine the catalytic mechanism of the folate- dependent de novo purine biosynthetic enzyme, glycinamide ribonucleotide transformylase. A series of kinetic studies, substrate specificity studies, affinity labeling studies, and site-directed mutagenesis studies are described. The aim of these studies is to define the kinetic and chemical mechanism of the transformylation reaction and to identify the enzyme residues involved in substrate binding and catalysis. These studies will afford mechanistic and structural information about the transformylase which will provide a basis for the design of specific transformylase inhibitors. These studies will also serve as the foundation for future studies on the interactions of the enzymes which constitute the de novo purine biosynthetic pathway and the mechanism(s) of regulation of the pathway. Although it has been demonstrated that inhibition of this pathway shows potential for cancer chemotherapy, much basic information about the pathway and the individual enzymes which constitute the pathway remains to be elucidated.